Conventionally, turbine engines firstly comprise, starting from upstream, one or more compressor modules which are arranged in series and compress the air sucked into an air inlet. The air is then introduced into a combustion chamber where it is mixed with a fuel and burned. The combustion gases pass through one or more turbine modules which drive the compressor(s). The gases are lastly ejected either into an exhaust nozzle to produce a propulsive force or onto a free turbine to produce the power which is recovered from a propeller shaft.
The current bypass turbojet engines having a high bypass ratio, or turbofans, comprise a fan rotor and a plurality of compressor stages, in particular a low-pressure (LP) compressor and a high-pressure (HP) compressor which belong to the primary body of the engine. Upstream of the low-pressure compressor, a large movable-blade wheel, or a fan, is arranged, which supplies both a primary duct with a primary flow passing through the LP and HP compressors and a secondary duct with a cold flow, or secondary flow, which is directed directly towards a cold-flow exhaust nozzle, referred to as the secondary exhaust nozzle. The fan is driven by the rotating shaft of the LP body and generally rotates at the same speed as said shaft. However, it may be advantageous to rotate the fan at a rotation speed which is lower than that of the LP shaft, in particular when said fan is very large, in order to better adapt it aerodynamically. For this purpose, a reduction gear is arranged between the LP shaft and a fan shaft which supports the fan. Such a design is described in particular in FR 20120051655 and FR 20120051656, which were filed on 23 Feb. 2012.
The turbojet engine having a speed reduction gear thus has clear advantages, but some difficulties must still be overcome.
In particular, said reduction gear must be lubricated and cooled in order to ensure the proper operation thereof without being damaged. Nowadays, it is estimated that the amount of oil required to ensure the operation of a turbojet engine equipped with a speed reduction gear is two times greater than in the case of a turbojet engine without a speed reduction gear. This oil makes it possible in particular to fulfil the functions of lubricating and cooling the movable components of the turbine engine.
It is known to cool said oil by means of an air/oil surface exchanger, which is also known by the name “SACOC”, an abbreviation of the term “surface air cooled oil cooler”. The exchange surface area is generally formed in a channel for circulating air of the turbojet engine. In said exchanger, a plurality of channels are provided in which the oil to be cooled circulates. The heat exchange is carried out by thermal conduction through the walls of the channels. Thus, the air and oil are not mixed.
In known heat exchangers, the heat exchanger is arranged in the secondary duct of the turbojet engine, downstream of the fan. In turbojet engines which are designed without a speed reduction gear, the rate of air flow which is required to cool the oil is low enough that it does not cause substantial pressure losses in the secondary duct.
However, turbojet engines equipped with a speed reduction gear require a much greater rate of air flow, for example two times greater than the rate of air flow of a turbojet engine without a speed reduction gear.
FR B1 2.965.299 is known, which relates to the lubrication of antifriction bearings, in which the oil is contained in lubrication chambers which are kept under excess pressure relative to the surrounding cavities in order to ensure that the oil is kept inside the lubrication chambers. Said excess pressure is achieved by injecting compressed air into the chamber. Said compressed air also makes it possible to produce a mist of oil, which allows a uniform distribution of the oil over the components of the turbine engine which is to be lubricated. In order to prevent the compressed air from having an overly high temperature in order to allow effective cooling of the components, this document proposes taking off the air upstream of the fan.
However, the air taken off is not cold enough to ensure, on its own, an effective cooling of the lubrication and cooling oil. Furthermore, the air is sucked into the oil chambers by means of a jet pump, which makes it necessary to take off air in the primary duct. The operation of such a device is thus liable to disrupt the flow of air in the primary duct, in particular when the amount of air to be taken off is significant.
U.S. Pat. No. 4,722,766 is also known, which describes and shows a device for cooling the lubrication oil of a reduction gear of a turbine engine. Said device comprises a fan rotor which is mounted so as to rotate about an axis of rotation which comprises a hub and a cone which is mounted upstream of the hub and in which is formed an air take-off opening which opens into an air channel which supplies a pump for driving the air, which is driven by the engine and is intended to power an exchanger in which the oil of the reduction gear circulates.
The air taken off at the surface of the cone by said opening and said channel is taken off having a rate of flow which is insufficient to ensure that the exchanger has a sufficient supply, to such an extent that it is necessary to pump said air by means of a mechanical pump, which thus takes off some of the power from the turbine engine.
The invention remedies this drawback by proposing a turbine engine fan rotor comprising improved means for taking off the air upstream of the fan.